DE60028737T2 - ELECTRICALLY CONDUCTIVE FLEXIBLE COMPOSITION, PROCESS FOR THEIR PREPARATION - Google Patents

Abstract

An electroconductive composition comprising an elastic matrix material and particulate filler material dispersed therein, the particulate filler material comprising fiber particles coated with a conductive material and spheroidal particles coated with a conductive material, the dispersion being such that the fiber-containing particulate filler and the spheroid-containing particulate filler are substantially interspersed, the particulate filler being present in an amount such that the conductive-material coated particles are in electroconductive relationship and such that the composition possesses enhanced flexibility, the conductive material being present in an amount sufficient that the composition has a decreased resistivity. The invention also encompasses a method of preparing these compositions comprising the steps of compounding said filler into a precursor of said flexible matrix material thereby dispersing said fillers throughout the matrix material, and curing the precursor to form the matrix.

Description

Territory of invention

The The invention relates to electrically conductive compositions which are flexible, materials for their production, which are easily moldable are, and process for their preparation. The invention relates also articles of manufacture, made of electrically conductive Compositions are formed, for. B. shaped objects and injection-molded objects such as B. seals.

It will be different publications cited, which more fully describe the prior art related to the invention and incorporated herein by reference.

background the invention

With continued advances in industrial technology and of the general standard of living have the uses of electromagnetic Energy increased and the number of sources for generating a such energy has multiplied at the same time. The exit Electromagnetic radiation into the environment has become one significant problem.

A Technology that governs the conduction of electromagnetic energy a predetermined, well-defined way requires, for. In waveguide applications, For example, it is increasingly becoming an important component of modern life Communications and other technologies. These waveguide applications require a quantitative limitation of electromagnetic Radiation for the effective implementation of the selected technology. The exit The electromagnetic radiation can achieve the desired results considerably to disturb.

Further is the leakage of electromagnetic radiation per se for life forms and another plant occupying the same environment is harmful. Except that they adverse influences on the human body has, the emitted radiation can also be an unpredictable behavior and / or damage of integrated circuits and an electronic system. Electromagnetic waves coming from electronic computers in different office equipment can be broadcast for example, disrupt the performance of televisions and an audio system.

It It has long been known that various electrically conductive materials can be used to to absorb or reflect electromagnetic waves and Consequently, to restrict electromagnetic radiation or other system or to shield a plant from it. Examples are metals that are electromagnetic Waves can absorb or reflect, and plastics, on where such metals are deposited.

compositions the metallic conductive fillers contained in quantities that are large enough to get a good electrical conductivity can ensure but subject to other difficulties. Both the costs as also the specific gravity are usually higher than desired. The amount of filler, which is necessary to ensure the electrical conductivity can also on the flexibility the compositions and the formability of precursor materials, from which the compositions are prepared (eg, fluidity, such as B. Moldability of a paste from which the composition is formed will). It is known, metallic particles by particles with a non-metallic core or substrate that is with a electrically conductive Material is coated, replace. Although this aid can drive down costs and specific gravity, it is not problem free. This is due to the persistence of a fundamentally problematic one Bifurcation, the introduction of conductive fillers loaded in flexible matrix materials, namely: when the conductive filler in smaller quantities is added to the flexibility and moldability to preserve, becomes the conductive Effect undesirable reduced; however, if the filler In larger quantities for one high conductivity is added, the flexibility and moldability (eg Strength, moldability).

For example, attempts to make polymer materials electrically conductive have had less than even success. The molding of polymers incorporating conductive fibers has been attempted, but in order to achieve acceptable electrical conductivity, so much fiber must be added that there is a significant reduction in certain other desirable polymer properties (such as those, e.g. concerning flexibility and / or malleability). Silver or other metal flakes and metal coated glass spheres have also been added to polymers, but again very high levels of Bela levels required to achieve electrical conductivity, which is unaffordable for most applications and can interfere with the desired achievement of all properties.

• – Das US-Patent Nr. 3 140 342 beschreibt ein Verfahren, das bei der Herstellung von leitfähigen Kunststoffgegenständen mit Hochfrequenz-Abschirmungsfähigkeiten verwendet wird. Metallpartikel werden mit der ungehärteten Phase eines komprimierbaren Harzes vermischt und die Masse wird dann gehärtet. Der Kontakt von Partikel zu Partikel stellt zahlreiche leitfähige Wege durch den gehärteten Gegenstand mit einer resultierenden hohen Leitfähigkeit bereit. Die Kosten des leitfähigen Kunststoffs sind jedoch aufgrund der hohen Konzentration von Metall darin ziemlich hoch, insbesondere wenn ein teures Metall wie z. B. Silber verwendet wird. Mit einer hohen Metallkonzentration werden überdies viele der erwünschten physikalischen Eigenschaften des Kunststoffs erheblich abgeschwächt. Folglich kann der fertig gestellte Gegenstand nicht so viel Zugfestigkeit wie gewünscht aufweisen und seine Komprimierbarkeit wird durch die große Anzahl von Verbindungsmetallpartikeln signifikant vermindert.
• – Das US-Patent Nr. 3 194 860 beschreibt ein Verfahren zur Herstellung von Dichtungen aus mit Metall gefülltem leitfähigem Kunststoff, wobei die flache Dichtung aus einer Platte von Kunststoffelastomer, das mit einem leitfähigen Metallpulver gefüllt ist, ausgestanzt wird. Die Pulverpartikel können feste Edelmetallpartikel oder Nicht-Edelmetall-Partikel wie z. B. Eisen oder Kupfer, das mit einem Edelmetallüberzug wie z. B. Silber oder Gold beschichtet ist, sein. Obwohl die Verwendung von Nicht-Edelmetall-Dichtungen, die mit Silber oder Gold beschichtet sind, einen weniger kostspieligen leitfähigen Kunststoff bereitstellt, vermindern hohe Beladungen, die häufig erforderlich sind, um den Kunststoff leitfähig zu machen, andere erwünschte physikalische Eigenschaften des Kunststoffs, wie z. B. Komprimierbarkeit und Zugfestigkeit.
• – Das US-Patent Nr. 4 500 447; US-Patent Nr. 4 557 859; US-Patent Nr. 4 642 202; US-Patent Nr. 4 765 930; US-Patent Nr. 4 822 089 und US-Patent Nr. 5 430 085 beschreiben elektrisch leitfähige Zusammensetzungen, in denen Kohlenstoff das elektrisch leitfähige Material ist. Der in diesen Bezugsquellen angeführte Kohlenstoff kann Ruß sein, der üblicherweise in elektrisch leitfähigen Silikonkautschuken oder als Teil eines Systems, das andere Metalle umfasst, verwendet wird. Die Metalle können Al, Zn, Fe, Ni, Sn, Pb und Ag als Kugeln, Plättchen oder Whisker sein. Der Kohlenstoff kann als Fasern oder Filamente, unbeschichtet oder beschichtet mit Metall durch Elektroabscheidung, verwendet werden. Eine stark elektrisch leitfähige Zusammensetzung mit einem niedrigen spezifischen elektrischen Volumenwiderstand wird jedoch nicht leicht mit solchen Verfahren erreicht. Wenn Polymere mit Kohlenstofffasern beladen werden, um eine annehmbare elektrische Leitfähigkeit zu erreichen, muss jedoch so viel Kohlenstofffaser zugegeben werden, dass eine merkliche Verringerung der anderen erwünschten Qualitäten wie z. B. Polymerflexibilität und Precursor-Formbarkeit besteht. Aufgrund der großen Differenz des spezifischen elektrischen Widerstandes zwischen Kohlenstoff und Metallen wie z. B. Silber können überdies mit Kohlenstofftasern gefüllte Polymere nicht den spezifischen elektrischen Widerstand bereitstellen, der für die EMI-Abschirmung erforderlich ist. Wenn Kohlenstofffasern, die mit elektrisch leitfähigem Metall beschichtet sind, verwendet werden, ist ebenso die resultierende elektrische Leitfähigkeit nicht gleichmäßig und kontinuierlich. Dies wird teilweise durch die schlechte Haftung des Metalls an den Kohlenstofffasern verursacht.
• – Das US-Patent Nr. 5 214 091 beschreibt mit Silber beschichtete Glaskügelchen, die ein Beispiel für leitfähige anorganische Füllstoffe sind, die für den Zweck des gleichzeitigen Erreichens einer annehmbaren Leitfähigkeit mit niedrigeren Kosten als feste Edelmetallpartikel und auch zum Vermeiden der mit der Verwendung von Kohlenstoff verbundenen Nachteile modifiziert sind. Um die gewünschte Leitfähigkeit bereitzustellen, ist es jedoch erforderlich, eine allzu große Menge an leitfähigem anorganischen Füllstoff zuzugeben.
• – Das US-Patent Nr. 5 672 297 beschreibt die Verwendung von Gelpartikeln in einem gequollenen Zustand, um ausdehnbare und zusammenziehbare Matrizes auszubilden. Die leitfähigen Verbundgegenstände, die aus diesen Mat rizes hergestellt werden, können als elektrische "Ein-Aus"-Schalter verwendet werden. Die in dieser Bezugsquelle offenbarte Matrix enthält leitfähige Füllpartikel mit regelmäßiger oder unregelmäßiger Form, wie z. B. Kügelchen-, Faser- oder Flockenformen. Eine Kombination von zwei oder mehr leitfähigen Füllpartikeln ist beschrieben. Beispiele von Füllpartikeln umfassen Kupferpulver, mit Silber beschichtete Nickelflocken, mit Silber beschichtete Glasblasen, feste Glaskügelchen, Glimmerflocken und Kohlenstoffpulver. Der resultierende Gelmatrix-Verbundstoff besitzt einen hohen spezifischen elektrischen Widerstand und unterliegt einer signifikanten Änderung im Ansprechen auf unbedeutende Veränderungen in einem von mehreren extern gesteuerten thermodynamischen Parametern, wie z. B. Temperatur, pH-Wert, Ionenstärke und Lösungsmittelzusammensetzung. Die Lehren des Patents sind zum Lehren der Erfindung ungeeignet, da die von diesem offenbarten Gelmatrix-Verbundstoffe für Dichtungen oder als Abschirmung gegen elektromagnetische Strahlung nicht nützlich wären, die Zugabe von anorganischen Füllstoffen gewöhnlich eine lokale Änderung der elektrischen Leitfähigkeit aufgrund einer unzweckmäßigen Verteilung von Füllstoffen verursacht und die Zugabe von großen Mengen von solchen anorganischen Füllstoffen auch die Flexibilität und Formbarkeit der Polymerzusammensetzung beeinträchtigt, was sie schwierig zu formen macht.
• – Das US-Patent Nr. 4 816 184 offenbart thermoplastische Harzpellets, die zum Formen zu Gegenständen mit einem Abschirmeffekt für elektromagnetische Wellen verwendet werden. Die Pellets besitzen einen Kern aus Glasfasern, der mit Metall beschichtet ist, das sich von einem Ende des Pellets zum anderen erstreckt. Der Kern ist von thermoplastischem Harz mit anderen leitfähigen Pulvern, Flocken oder kurzen Füllstoffen, die darin verteilt sind, umgeben. Um eine nützliche elektrische Leitfähigkeit zu erreichen, sind jedoch hohe Beladungsniveaus erforderlich. Fasern richten sich überdies gewöhnlich innerhalb einer Polymermatrix aus, was Steifigkeit in der resultierenden Zusammensetzung und eine gleichzeitige Verringerung der Flexibilität verursacht.

More specific examples of the foregoing are as follows:

• US Patent No. 3,140,342 describes a method used in the manufacture of conductive plastic articles having radio frequency shielding capabilities. Metal particles are mixed with the uncured phase of a compressible resin and the mass is then cured. Particulate to particle contact provides numerous conductive paths through the cured article with a resultant high conductivity. However, the cost of the conductive plastic is quite high due to the high concentration of metal therein, especially if an expensive metal such. As silver is used. Moreover, with a high metal concentration, many of the desirable physical properties of the plastic are significantly attenuated. Consequently, the finished article may not have as much tensile strength as desired and its compressibility is significantly reduced by the large number of interconnect metal particles.
• US Pat. No. 3,194,860 describes a method of making gaskets of metal-filled conductive plastic, wherein the gasket is punched out of a sheet of plastic elastomer filled with a conductive metal powder. The powder particles may solid metal particles or non-noble metal particles such. As iron or copper, with a noble metal coating such. As silver or gold, be. Although the use of non-precious metal seals coated with silver or gold provides a less expensive conductive plastic, high loadings often required to render the plastic conductive reduce other desirable physical properties of the plastic, such as plastic , B. compressibility and tensile strength.
• US Pat. No. 4,500,447; U.S. Patent No. 4,557,859; U.S. Patent No. 4,642,202; U.S. Patent No. 4,765,930; U.S. Patent No. 4,822,089 and U.S. Patent No. 5,430,085 describe electrically conductive compositions in which carbon is the electrically conductive material. The carbon referred to in these references may be carbon black, which is commonly used in electrically conductive silicone rubbers or as part of a system comprising other metals. The metals may be Al, Zn, Fe, Ni, Sn, Pb and Ag as spheres, platelets or whiskers. The carbon may be used as fibers or filaments, uncoated or coated with metal by electrodeposition. However, a highly electrically conductive composition having a low volume resistivity is not easily achieved by such methods. However, when polymers are loaded with carbon fibers to achieve acceptable electrical conductivity, so much carbon fiber needs to be added that there is a significant reduction in other desirable qualities, such as carbon fibers. B. polymer flexibility and precursor formability. Due to the large difference in the specific electrical resistance between carbon and metals such. In addition, for example, silver can not provide carbon fiber filled polymers with the resistivity required for EMI shielding. Also, when carbon fibers coated with electrically conductive metal are used, the resulting electrical conductivity is not uniform and continuous. This is partly due to the poor adhesion of the metal to the carbon fibers.
• US Pat. No. 5,214,091 describes silver-coated glass beads which are an example of conductive inorganic fillers used for the purpose of simultaneously achieving acceptable conductivity at a lower cost than solid precious metal particles and also avoiding the use of Carbon-related disadvantages are modified. However, in order to provide the desired conductivity, it is necessary to add an excessive amount of conductive inorganic filler.
• U.S. Patent No. 5,672,297 describes the use of gel particles in a swollen state to form expandable and contractible matrices. The conductive composite articles made from these materials can be used as electrical "on-off" switches. The matrix disclosed in this reference contains conductive filler particles of regular or irregular shape, such as e.g. B. bead, fiber or flake shapes. A combination of two or more conductive filler particles is described. Examples of filler particles include copper powder, silver-coated nickel flakes, silver-coated glass bubbles, solid glass beads, mica flakes and carbon powder. The resulting gel matrix composite has a high resistivity and undergoes a significant change in response to insignificant changes in one of several externally controlled thermodynamic parameters, such Temperature, pH, ionic strength and solvent composition. The teachings of the patent are unsuitable for teaching the invention, since the gel matrix composites disclosed by it would not be useful for seals or electromagnetic radiation shielding, the addition of inorganic fillers usually causes a local change in electrical conductivity due to inappropriate spreading of fillers and the addition of large quantities of such inorganic fillers, too the flexibility and malleability of the polymer composition is compromised, making it difficult to mold.
• US Pat. No. 4,816,184 discloses thermoplastic resin pellets used to mold into articles having an electromagnetic wave shielding effect. The pellets have a glass fiber core coated with metal extending from one end of the pellet to the other. The core is surrounded by thermoplastic resin with other conductive powders, flakes or short fillers dispersed therein. However, to achieve useful electrical conductivity, high loading levels are required. Fibers, moreover, usually align within a polymer matrix, causing rigidity in the resulting composition and a concomitant reduction in flexibility.

• – Das US-Patent Nr. 4 777 205 richtet sich auf eine Organopolysiloxan-Zusammensetzung, die mit Silber beschichtete Glimmerpartikel und Ruß, einen Platinkatalysator und einen Platin-Katalysator-Inhibitor sowie halb oder nicht verstärkende nicht leitfähige Füllstoffe, einschließlich Glaskügelchen, -blasen oder -fasern, enthält. Es ist zu beachten, dass Glimmer ein Material ist, das nicht das Niveau an spezifischem elektrischen Widerstand bereitstellen kann, das für Dichtungen, die bei der EMI-Abschirmung nützlich sind, erforderlich ist.
• – Das US-Patent Nr. 4 357 266 offenbart ein elektrisch isolierendes Polymermaterial wie z. B. Diorganopolysiloxan, das einen fein verteilten teilchenförmigen Stoff oder Fibrillen von metallischem Silicium beinhaltet. Die in dieser Bezugsquelle beschriebene Matrix enthält ein mono- oder difunktionelles Silikon, um die Widerstandsfähigkeit aufrechtzuerhalten, wenn ein geformter Kautschukgegenstand einer Biege- oder Schwingungsbeanspruchung ausgesetzt wird.
• – Das US-Patent Nr. 5 227 093 richtet sich auf eine Organosiloxan-Zusammensetzung (mit einem Platinkatalysator gehärtet), die Silber oder mit Silber beschichtete Partikel enthält, die vor ihrer Integration mit einem Fettsäureester behandelt werden.
• – Das US-Patent Nr. 4 836 955 offenbart ein Silikonbindemittelsystem (mit einem Vinylgummityp von Silikonharz als erster Komponente und einem flüssigen Silikonharz als zweiter Komponente), das mit Silber überzogene Kupferpartikel enthält, zur Verwendung als Dichtung, wobei eine solche Formulierung eine verbesserte elektrisch leitfähige Stabilität aufweist, wenn die Partikel einer Langzeit-Wärmebehandlung vor ihrer Integration in die Matrix unterzogen werden. Mit Silber beschichtete Kupferpartikel sehen jedoch einen dichten Füllstoff vor. Um einen spezifischen elektrischen Widerstand zu erhalten, der zu mit Silber beschichteten Glasfüllstoffen vergleichbar ist, sind wesentlich mehr Kupferpartikel erforderlich. Folglich werden die Flexibilität und die Formbarkeit der Dichtung beeinträchtigt. Überdies sind mit Silber beschichtete Kupferpartikel sehr teuer.
• – Das US-Patent Nr. 5 075 038 beschreibt eine Anzahl von verschiedenen Ausführungsformen, wie z. B. einen druckempfindlichen Siloxansilikon-Klebstoff, der mit Silber überzogenes Kupferpulver enthält, einen elektrisch leitfähigen Werkstoff mit einem Gemisch aus Siloxanpolymer mit einem Härtungsmittel (Aminosilan oder Aminosilazan) und elektrisch leitfähigen Partikeln mit einer äußeren Oberfläche aus Edelmetall, Vinyl enthaltende Organopolysiloxane und Organopolysiloxane mit Si-gebundenen Wasserstoffatomen zusammen mit einem Katalysator und einem leitfähigen Material, eine Polymerzusammensetzung (z. B. ein Epoxidharz, Silikon, Fluorsilikon, Polyurethan oder langkettiger Kohlenwasserstoff), die mit Silberflocken beladen ist, und eine Silikonzusammensetzung, die unter Verwendung eines Platinkatalysators und eines Silikonpolymers mit Mengen an aromatischen Stoffen enthaltenden Resten oder ethylenisch ungesättigten Kohlenwasserstoffresten (z. B. Vinylresten zusätzlich zu jenen, die üblicherweise als Endblocker verwendet werden), sowie Silberpartikeln oder mit Silber beschichtetem Kupfer, festem Glas, hohlem Glas, Glimmerflocken, Nickelkörnchen und -kugeln, kurzer Glas- und Keramikfaser gebildet wird.
• – Ferner beschreibt das US-Patent Nr. 5 229 037 mehrere Systeme, wie z. B.: eine stark elektrisch leitfähige Silikonkautschuk-Zusammensetzung, die Edelmetallpulver oder ein anorganisches Material (beispielsweise Glas, Glimmer, Aluminiumoxid, Kohlenstoff und dergleichen), das mit Silber, Nickel usw. beschichtet oder überzogen ist, enthält; eine Silikonkautschuk-Zusammensetzung, die durch Vermischen eines metallischen, elektrische Leitfähigkeit verleihenden Mittels mit einer isolierenden Silikonkautschuk-Zusammensetzung in Kombination mit einem feinen Pulver oder einem gehärteten Silikonkautschuk (oder alternativ Ruß) erhalten wird; und eine elektrisch leitfähige Zusammensetzung mit einem Diorganopolysiloxan, kugelförmigen Partikeln eines gehärteten Silikonelastomers, einem metallischen, elektrische Leitfähigkeit verleihenden Mittel in fein verteilter Form und einem Härtungsmittel sowie (wahlweise) einer flüssigen Organosilikon-Verbindung.

Of particular interest are conductive compositions having a silicone-based matrix system, which are appreciated for their superior elastomeric properties, yet have not been successfully made highly conductive without diminishing flexibility, as follows:

• U.S. Patent No. 4,777,205 is directed to an organopolysiloxane composition comprising silver-coated mica particles and carbon black, a platinum catalyst and a platinum catalyst inhibitor, and semi or non-reinforcing non-conductive fillers, including glass beads, bubbles or fibers. It should be noted that mica is a material that can not provide the level of resistivity required for gaskets useful in EMI shielding.
• US Pat. No. 4,357,266 discloses an electrically insulating polymeric material, such as Diorganopolysiloxane containing a finely divided particulate or fibrils of metallic silicon. The matrix described in this reference contains a mono- or difunctional silicone to maintain resistance when a molded rubber article is subjected to bending or vibration stress.
• U.S. Patent No. 5,227,093 is directed to an organosiloxane composition (cured with a platinum catalyst) containing silver or silver-coated particles which are treated prior to their integration with a fatty acid ester.
• US Patent No. 4,836,955 discloses a silicone binder system (having a vinyl rubber type of silicone resin as a first component and a liquid silicone resin as a second component) containing silver-coated copper particles for use as a gasket, such formulation being an improved electric has conductive stability when the particles are subjected to a long-term heat treatment prior to their integration into the matrix. However, silver-coated copper particles provide a dense filler. To obtain a resistivity comparable to silver-coated glass fillers, significantly more copper particles are required. As a result, the flexibility and moldability of the gasket are impaired. Moreover, silver-coated copper particles are very expensive.
• US Pat. No. 5,075,038 describes a number of different embodiments, such as: For example, a pressure-sensitive siloxane silicone adhesive containing silver-coated copper powder, an electrically conductive material comprising a mixture of siloxane polymer with a curing agent (aminosilane or aminosilazane) and electroconductive particles having a noble metal outer surface, organopolysiloxanes containing vinyl, and organopolysiloxanes containing Si bonded hydrogen atoms together with a catalyst and a conductive material, a polymer composition (e.g., an epoxy resin, silicone, fluorosilicone, polyurethane or long chain hydrocarbon) loaded with silver flakes, and a silicone composition formed using a platinum catalyst and a silicone polymer containing residues of aromatic species or ethylenically unsaturated hydrocarbon radicals (e.g., vinyl radicals in addition to those commonly used as endblockers), as well as silver particles or silver copper, solid glass, hollow glass, mica flakes, nickel granules and spheres, short glass and ceramic fiber.
• Furthermore, US Pat. No. 5,229,037 describes several systems, such as. B: a highly electroconductive silicone rubber composition containing noble metal powder or an inorganic material (e.g., glass, mica, alumina, carbon and the like) coated or coated with silver, nickel, etc.; a silicone rubber composition obtained by blending a metallic electrical conductivity imparting agent with an insulating silicone rubber composition in combination with a fine powder or a cured silicone rubber (or alternatively carbon black); and an electrically conductive composition comprising a diorganopolysiloxane, spherical particles of a cured silicone elastomer, a metal electroconductive agent in finely divided form and a curing agent, and (optionally) a liquid organosilicone compound.

The foregoing disclosures illustrate attempts at loading silicone rubber materials. In general, these materials have excellent hot and cold resistance and weatherability, as well as excellent electrical insulation properties, so that they are widely used in a variety of applications. Electrically conductive silicone rubbers having a volume resistivity of 10 ^-4 to 10 ⁶ ohm.cm were prepared by mixing an insulating silicone rubber precursor with a substantial amount of an electroconductive agent and curing to form the silicone rubber. Typically, gaskets or compositions intended for EMI shielding have a volume resistivity of 10 ^-3 to 10 ^-2 ohm.cm. Although such rubbers are in and of themselves reasonably flexible, and are typically made from precursor materials that are reasonably moldable, at load levels required to impart high conductivity to the end products, these properties can be unacceptably reduced.

Summarized: the formability and flexibility are important considerations, if the goal is flexible sealing rings or gaskets to train for Waveguide arrangements, weatherproof RF enclosures and the like are useful, or a relatively lightweight shield for protecting sensitive electronic devices from higher levels of electromagnetic Radiation in the environment due to increased use of electronic To train investment. On return to waveguide applications need the materials used, for example, a high electrical conductivity and impermeability for the have electromagnetic energy in the waveguide to be an effective part the waveguide structure to act. Likewise, materials must be considered high frequency shielding used, very conductive and for be impermeable to electromagnetic radiation at the relevant frequencies, for a sensitive electronic instrumentation foreign electromagnetic energy present in the environment. The characteristics of flexibility and precursor moldability, however, are also in each of the above mentioned Application important so that (for example) a conductive object, which is formed of such a material, in contact with a can be configured and / or held manipulatable element, around the required zone of limitation of the electromagnetic Energy for the waveguide path or the exclusion of energy from the shielded ones Provide components. (It goes without saying that such properties also for the achievement of a liquid or airtight seal, for example as by a flexible electrically conductive Seal provided between a pair of engaged Parts are important.) It is such previously produced materials disadvantageously holding that a compromise between the flexibility on the one hand and the electrical conductivity, on the other hand consists. When a more electrically conductive filler is added to the matrix material becomes, the conductivity decreases material, but the flexibility decreases. High filler loadings, considered necessary to achieve sufficient conductivity Beyond that limit, too the processing versatility of a material, such. B. his compatibility with injection molding. Various attempts have been made to those described above To solve problems, but without satisfactory results.

One Material that has both good electrical conductivity and good flexibility (or in the case of a precursor good moldability), as above called, would the field of activity is considerably forward bring.

Tasks of invention

It It is an object of the invention to overcome the difficulties identified above to eliminate.

It Another object of the present invention is a material with good flexibility to create, which is also electrically conductive.

It is yet another object of the present invention, a precursor material, having good formability, and in terms of manufacture an electrically conductive create flexible material out of it.

It Another object of the present invention is to provide methods for Preparation and use of the above-mentioned compositions and Precursor materials to accomplish.

It is yet another object of the present invention, products, which are formed from such compositions, including Seals, molded objects, injection-molded objects etc.

Various Other objects, advantages and features of the invention are apparent from the following description readily apparent.

Summary the invention

In In one aspect, the invention is an electrically conductive composition, an elastic matrix material and a distributed therein particulate filling material wherein the particulate filler comprises a plurality of particles with an elongated one Core or substrate that coats with a conductive material is, and a variety of particles with a spherical core or substrate that coats with a conductive material is included. The distribution of the particulate filling material in the matrix material is such that the elongated Particles and the spherical ones Particles are substantially mutually mixed, with the total amount of the particulate filler 40 to 70 weight percent of the composition is and the weight ratio of elongated Particles to the spherical ones Particles 1: 1 to 4: 1, so that coated with conductive material Particles are in an electromagnetic relationship and so that the composition is functionally flexible.

In In another aspect, the invention is an electrically conductive paste for forming a solidified flexible electrically conductive composition, wherein the paste is a precursor material that results in an elastic Matrix material is moldable, and particulate filler material contained in the precursor material is distributed, wherein the corpuscular filler comprises a plurality of Particles with an elongated Core or substrate that coats with a conductive material is, and a variety of spherical particles with a Core or substrate that coats with a conductive material is, includes, being the elongated Particles and spherical Particles are substantially mutually mixed, with the total amount of the particulate filler and the quantities of oblong and spherical conductive Particles relative to each other are such that, when the precursor material is formed into the matrix coated with conductive material Particles are in an electrically conductive relationship and the composition is functionally flexible.

The present invention makes of a plurality of electrically conductive particles Use a first part of particles that are essentially from an elongated one Core or substrate, the / with an electrically conductive material is coated, and a second part of particles, essentially from a spherical Core or substrate, the / with an electrically conductive material coated, wherein the two parts of particles in the Essentially mutually intermixed, with quantities of elongated ones Particles and spherical Particles relative to each other are such that when the particles in a composition consisting essentially of such particles and a substantially non-conductive flexible matrix material exists to be integrated in an amount that is effective to the Composition to impart electrical conductivity, the composition also functional flexibility having.

In In another aspect, the invention is an article of manufacture a molded element having an electrically conductive composition, such as defined above.

The Compositions of the present invention can be prepared by a process be the mixing of a particulate filler with a variety of oblong Particles with a core or substrate containing a conductive material is coated, and a plurality of spherical particles with a Core or substrate that coats with a conductive material is, in a precursor of a flexible matrix material such includes that elongated Particles and the spherical ones Particles in the precursor are substantially mutually mixed; subsequently if the precursor is hardened, to form the matrix; being the amount of the entire corpuscular filler and the amounts of the elongated conductive particles and spherical conductive Particles relative to each other are such that those with conductive material coated particles in the composition after curing in an electrically conductive relationship stand and the composition is functionally flexible.

The pastes of the present invention can be prepared by a method comprising blending a particulate filler having a plurality of elongated particles with a core or substrate coated with a conductive material and a plurality of spherical particles having a core or substrate Substrate, which is coated with a conductive material, in a precursor material, which is moldable into a flexible matrix material, so that the elongated particles and the spherical particles in the precursor are substantially mutually mixed comprises. The total amount of the particulate filler and the amounts of the elongated particles and spherical particles relative to each other are the such that when the precursor material is formed into the matrix, the conductive material coated particles in the composition are in an electrically conductive relationship and the composition has functional flexibility.

The Invention is to provide a shield, conductive components, Elements for the discharge of an electrostatic charge and others Articles of manufacture where good electrical conductivity and flexibility necessary or advantageous, useful.

The Practice according to the invention leads to noticeable advantages. The good conductivity is due to the integration a considerable one Flock of corpuscular conductive filler reached. Furthermore becomes an economy through the use of conductive fillers achieved largely from one or more relatively inexpensive Consist of substances that typically act as a nucleus or substrate, and which is essentially complete or in an effective part with an electrically conductive material usually covered (although not necessarily) more expensive than the above said (n) Substance (s). In this way, the amount of more expensive material compared to embodiments be reduced, in which the conductive filler completely (or mainly) from one or more relatively expensive electrically conductive substances consists. moreover Can the corpuscular conductive filler of the invention are formulated such that its specific gravity relatively lower than that of solid metal fillers, with the advantageous result that the specific gravity of with the filler The compositions loaded with the invention are also lower. And despite the use of appreciable amounts of particulate conductive filler, around the aforementioned Nevertheless, to ensure advantages, the invention also creates one Way to maintain an effective level of flexibility Matrix material and the own formability of a precursor paste, in the filler is distributed.

By execution within the invention hence all the competing concerns that in the preceding paragraphs discussed are, solved become.

Description of specific preferred embodiments the invention

introductory It can be seen that those used in the present invention Matrix materials are suitable for those who use in applications be, for the flexibility he wishes is, or those are the otherwise elastomeric properties demonstrate. Such materials include rubbers, such as. Fluorosilicone, EPDM (ethylene propylene diene monomer) and thermoplastic polyurethane. Of particular interest are silicone-based matrix systems, which be appreciated because of their elastomeric properties. Materials on Silicone base allow the production of molded electrically conductive bodies suitable for applications are suitable, which require high flexibility. Dependent on from the formulation of the matrix these can be used to produce, such as B. conductive Seals, shields, conductive Adhesives and the like.

The Matrix is made of a curable Precursor material formed. This material is typical a substance or substances (such as a system) that, when they a condition such as As catalysis, heat, irradiation with ultraviolet light or the like is exposed - in a solidified flexible Material can be converted. In and of itself are the choices and Processing of precursor materials to form the matrices, in the execution useful in the invention are known in the art. As an example, see in general those discussed above Revelations in the background the invention". A common one One skilled in the art, once provided with the teachings herein, can such knowledge of precursor materials to the practice of the invention without excessive experimentation or adapt further invention.

The above-noted polysiloxane matrix materials of interest are formed from a curable siloxane precursor system and typically comprise a non-conductive polymeric substance in which the electrically conductive filler material can be dispersed to impart electrical conductivity. The term "polysiloxane" refers to the major component of the polymeric substance, but does not exclude the presence of other substances. Thus, a polysiloxane matrix contains a plurality of different siloxane units, each repeating over the entire material, such units typically being substituted with one or more organic radicals, along with other components, such as e.g. A curing agent, a catalyst or one or more catalyst inhibitors, and ingredients for improving the workability of the curable precursor system or one or more of the properties of the cured material prepared from such a system. Additional ingredients in this last category include, but are not limited to, reinforcing fillers, such as: Finely divided silica, non-reinforcing fillers, filler treating agents, adhesion promoters, Flame retardants, heat stabilizers, pigments and dyes. Depending on the degree of polymerization, the viscosity of the precursor siloxane component used in the curable system may range from that of a flowable liquid to that of a relatively viscous gel or resin, although it is important in certain good embodiments of the invention the precursor has sufficient moldability so that it can be used in injection molding operations and the like. The selected siloxane components will depend on the desired processes and curing conditions in addition to the physical properties sought in the cured matrix. As stated so far, the polysiloxane matrix technology, including its formation from a siloxane component, is known per se and one of ordinary skill in the art may use suitable matrix materials depending on the desired physical properties and precursor siloxane components for production select it without undue experimentation or further invention.

In still other good embodiments The invention uses fluorosilicones. This offers the advantages of both silicones and fluorocarbons (silicones) discussed in the preceding paragraphs; the Fluorination of compounds often improves their thermal stability). In the case of siloxanes begins fluorination usually in the gamma position of a substituent alkyl chain (due to the electropositive Type of silicone can increase the fluorination in the alpha and beta positions lead to poor thermal stability). consequently For example, commercial fluorosilicones are often substituted with trifluoropropyl Methyl materials.

Examples of silicone-based matrix materials used in the present Invention useful are: elastomeric thermoplastic polyblock-organopolysiloxane copolymer (formed in a reaction catalyzed by platinum chloride derivatives as described in U.S. Patent No. 4,822,523; Organopolysiloxanes siloxanes as described in U.S. Patent No. 4,777,205 and U.S. Patent No. 5,227,093; a silicone binder system with a vinyl rubber type of silicone resin as the first component and a liquid silicone resin as the second Component as in the US patent No. 4,836,955; a pressure-sensitive siloxane silicone adhesive, an electrically conductive Material with a mixture of siloxane polymer with a curing agent (Aminosilane or aminosilazane), vinyl-containing organopolysiloxanes and organopolysiloxanes having Si-bonded hydrogen atoms, a Polymer composition (eg, an epoxy resin, silicone, fluorosilicone, Polyurethane or long-chain hydrocarbon) and a silicone composition, using a platinum catalyst and silicone polymer with residues of aromatic substances or ethylenically unsaturated hydrocarbon radicals (eg vinyl residues in addition to those who usually as endblocker), all as in the US Patent No. 5,075,038.

For the matrix The invention also several systems are useful, such as. B: a strong electrically conductive Silicone rubber; a silicone rubber composition used in an appropriate part by mixing an insulating silicone rubber composition in combination with a fine powder of a cured silicone rubber (or alternatively soot) is obtained; and a composition with a diorganopolysiloxane, spherical Particles of a hardened Silicone elastomers and a curing agent and (optionally) a liquid An organosilicone compound, all as described in U.S. Patent No. 5,229,037. Besides, they are for the Matrix of the invention useful: a vinyl-terminated polydimethylsiloxane optionally other polymer components and a hydrosyl group-containing polydimethylsiloxane for working as a curing agent contains as described in U.S. Patent No. 5,344,593; a system with one Organopolysiloxane having at least two alkenyl groups in its molecule, one Organohydrogenpolysiloxane with at least two silicone-bonded ones Hydrogen atoms in its molecule, a platinum-group metal catalyst, an organosilicone compound having at least one silicone-bonded Hydrogen atom and at least one bonded to silicone epoxy groups containing organic group or alkoxy group, as in the US patent No. 5,384,075; a silicone elastomer, for example by mixing vinylmethylsiloxane with a platinum catalyst with methylhydrogensiloxane, a teflon powder and a thermosetting one Silicone rubber system containing an inhibited platinum catalyst contains as disclosed in U.S. Patent No. 5,498,644; and a composition obtained by removing water from an emulsion with a dispersed phase of elastomer (eg based on of polydiorganosiloxane) and a continuous phase of water as disclosed in U.S. Patent No. 5,091,114.

In certain good embodiments of the present invention, the electrically conductive compositions of the invention also contain inorganic fillers such as e.g. Ordinary silica powder, colloidal silica, airgel silica, alumina or the like. Such fillers typically have a reinforcing function with a surface area of at least 50 m ² / g and / or fumed silica. The inclusion of such material gives the uncured mixture sufficient thixotropy, higher viscosity, and improved distribution stability of the electrically conductive material capable of imparting improved strength to the cured composition. In addition, in some other embodiments of the invention, it may be advantageous to include fillers that are semi-or non-reinforcing, ie, fillers that have a surface area of less than 50 m ² / g. Examples of semi or non-reinforcing fillers are metal oxides, metal nitrides, glass beads, bubbles or fibers, metal flakes, powders and fibers, such as e.g. Copper, nickel and aluminum cork, organic resins, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl chloride, bentonite, diatomaceous earth, crushed quartz, mica and mixtures thereof. These fillers may, for example, with trialkylalkoxysilanes such. For example, trimethylethoxysilane may be treated to coat the surfaces with organosiloxy groups.

Other Additives that are in the conductive Compositions of the invention can be integrated Pigments, compression set additives, oxidation inhibitors, plasticizers, Adhesion promoters, Base stabilizers and other materials commonly used as additives the silicone rubber field. The conductive composition The invention may also include a heat resistance improver such as As ceria, a flame retardant and non-functional Organopolysiloxanes for improving thermal shock resistance, flexibility and the like of the hardened Composition included.

In Consistent with the foregoing disclosure are curing methods on and for known. Consequently, curing is often accomplished by integrating one suitable catalyst component in the precursor material for the addition reaction, For example, to work as a curing accelerator, implemented. Such catalysts are also known in and of themselves and a common one One skilled in the art, once familiar with the teachings herein, may find suitable catalysts to achieve the desired hardening without excessive experimentation select the further invention. The catalyst may be, for example, any curing catalyst be that for the matrix precursors used in the compositions of the invention suitable is. In the present invention are mobile metal catalysts and organoperoxide catalysts among the preferred. helpful Noble metal catalysts include platinum and palladium for extrusion; useful Organoperoxide catalysts include dicumyl peroxide, dibenzoyl peroxide and MEK peroxide (methyl ethyl ketone peroxide).

The Method of adding the curing catalyst is not critical. The catalyst can be reacted with the siloxane component (s) for the Purpose of storage stability, the prevention of a uniform catalyst distribution etc. are mixed in advance. The catalyst is often used in the reaction mixture integrated at room temperature, although the catalyst at elevated Temperature can be added if desired. The amount of catalyst can by a usual Professional without exercise of a further invention, as soon as he learns with the teachings this invention is provided. This amount is typically based on the desired actual cure rate, Working life and the like.

One central feature of the present invention is the use a corpuscular filling material with both elongated as well as spherical conductive Particles. Each different particle shape, in a suitable Quantity is included for the realization of the advantage conferred by the invention is important. On the one hand are elongated Shapes are very advantageous in that their use to a reduced volume a relatively rigid filler should result in the composition (and in the precursor material), if they are distributed appropriately are. With the use of elongated Unfortunately, forms also run the risk of alignment and consequently Stiffness, which is the desired flexibility and formability usually reduced. Although the integration of spherical particles is the occurrence a directional one Alignment minimizes, on the other hand, the line between each Balls essentially point-point type and has the presence of a much larger quantity on rigid filling material, about the conductivity to achieve, as in elongated Particles result. This increases not only the amount of conductive metal required but reduced also the amount of matrix material, which is usually the malleability and flexibility impaired. The problem is solved by the present invention. It will believed that the inclusion of elongated conductive particles in combination with spherical conductive Particles to a beneficial disorientation of elongated Particles leads, to promote formability and flexibility. That is, while elongated Particles integrated alone in polymer matrices usually follow each other Orientate a single axis, are elongated particles in the Integrated polymer matrices in the presence of spherical particles are, usually fortuitously distributed or at least sufficiently little oriented that the composite material is not in a harmful Extent stiffened. As a result, moldability and flexibility become relatively high levels held. This is done while still a relative cost, highly electrically conductive Composition and a precursor material from which such Composition can be achieved.

The Use of spherical Particles together with elongated ones Particles leads furthermore, a composition with superior dimensional uniformity and stability compared to compositions that use only elongated particles. The physical effects of orientation of elongated Particles according to the invention are significant, for example. Elongated particles running along oriented on a single axis, selectively cause stiffness along this axis. The disorientation of elongated particles prevented a worsened stiffening along any axis and breaking instead effectively the stiffening effect of the elongated Particles on and spread this evenly over the whole matrix, resulting in flexibility contributes. Such a disorientation leads also to a more even electrical conductivity and a more even one specific electrical resistance.

The mentioned above Properties are characterized by a distribution of a mixture of spherical conductive particles and elongated ones conductive Reached particles in a suitable matrix. That the elongated Particles and spherical Particles "essentially are mixed together, should for the purposes of the present description mean that the elongated Particles more or less evenly under the spherical particles are distributed and vice versa. This condition occurs according to the invention not only when the particles are in the absence of one another Matrix material or precursors thereof are mixed, but Also, if the particles in this material or a precursor material are included. By reaching this mixing, the Advantages of the invention can be realized. Of course there can be local fluctuations, wherein the corpuscular filling material uncharacteristically concentrated or sparse, but these bodies should be in size and number limited so that the good qualities that come through the practice of Lent invention, not lost.

Of the Term "particle" or "particulate" as used herein refers to a small, discrete amount of substance; Although these Particle spherical or oblong are, must they are not complete be symmetrical and can indeed in different different places an irregular shape as long as the general elongated or spherical configurations be preserved. Typically, the particle comprises a core or a substrate of a suitable filling material and deposited thereon a suitably electrically conductive material. The shape of a conductive Particles is created by configuring such a kernel or Substrate determined. As a result, the elongated particles comprise a core or a substrate with a length, which is bigger as either the width or thickness. It is preferred that the elongated Core or the elongated one Substrate in the form of a rod or a fiber is present. As well include the spherical ones conductive Particles a spherical Core or a spherical one Substrate, which consists of a suitable filling material, and a Deposition of an electrically conductive material on the exterior. It is preferred that the spherical Core or the spherical one Substrate spherical or substantially spherical, for example, a spherical or substantially spherical beads is.

The elongate particles are any suitable filler material and are typically inorganic substance fibers. Likewise, the spherical particles are any suitable filler material; they are typically beads of an inorganic substance. The core or substrate of each electrically conductive particle is suitably an inorganic non-metallic material. This may be any of a wide range of materials having properties and physical properties consistent with achieving the objects of this invention. In this context, it is understood that "non-metallic" properties and physical properties are shown. Suitable materials typically exhibit non-electrically conductive properties. Consequently, these materials are typically glasses, ceramics and naturally occurring mineral substances. The following are examples of the foregoing materials: oxides, such as. B. bauxite, corundum, ilmenite, brookite, anatase, rutile and magnetite, and hydroxides, such as. B. brucite, sulfides, such as. Galena, pyrite, chalcopyrite and sphalerite; Halides, such as. Sodium chloride, sylvite and fluorite; Carbonates, such as. As calcite, magnesite and siderite, nitrates, such as. As sodium nitrate, and borates, such as. Borax and kernite; Sulfates, chromates and molybdate, examples being celestite, anhydrite and gypsum; and phosphates, such as. B. bivianite, apatite and pyromorphite, arsenates such. As erythritol, and vanadates, such as. B. Bavanadinite. Additional examples of suitable materials are conveniently classified into categories as follows: the tectosilicates, including the silica group, the feldspar group, the feldsparoid group, the zeolite group; the philosilicates, including kaolinite, talc and vermiculite, and the mica group, for example, muscovite, phlogovite and biotite; the inosilicates, including the amphibole group, for example the cummingtonite series, the pyroxene group, including the hypersthene series, for example spodumene, and the pyroxenoid group; the cyclosilicates, including beryl and tourmaline; the sorosilicate group, for example, Vesuvian; the neosilicates, including the olivine series, such as. Magnesium iron silicate, and also including willemite; the aluminum silicate group; the garnet group, and silicates with intermediate structure, such. Prehnite, chrysocolla and dumortierite. It goes without saying that synthetic as well as naturally occurring, inorganic, not metallic materials are suitable for carrying out the invention.

Of the elongated Core or the elongated one Substrate is typically a fiber. Its processing can often without The more stringent conditions are often used the aggregation are connected. On the other hand, the spherical core or the spherical one Substrate typically a bead. Frequently its heating up is pretty much to aggregate a material high temperatures are required and at such temperatures may be some the preceding materials, for example some of the hydroxides, Sulfides, halides, carbonates, nitrates and sulfates, in oxides being transformed. Consequently, the aggregation of these materials only with care, if any, carried out become.

In Embodiments, in which the conductive Particle core or the conductive Particulate substrate is glass, it is typical lime glass, a soda lime silicate glass composition, which is known in the art. The core or However, the substrate may also be suitably made of titanium glass or stronger for another fireproof glass for Applications that have special properties such. B. heat resistance, low alkali content and the like.

in the Generally, an inorganic non-metallic material, which is selected for use as a particle core or replacement, be such that the particles under processing conditions, which the precursor material of this invention in the manufacture of a electrically conductive body be subjected to it, not soften or noticeable in the Distort shape.

The Particles of inorganic non-metallic material are in made in any suitable manner. As an example a suitable method for the production of suitable fibers by extrusion through spinnerets. As another example, there is a suitable method of preparation of glass beads in it, crushed To introduce glass particles into a vertically arranged draft tube. The Pipe has a heat source near its lower end, usually a well-distributed gas flame, which is produced by a series of burners. When the combustion gases ascend, stream They move into an expansion chamber and carry the glass particles become soft, with it, leaving the particles by surface tension be formed into a spherical shape. The beads are then cooled and collected. Various bead preparation systems For example, U.S. Patent Nos. 3,279,905 and 18 October 1956 Thomas K. Wood et al. issued, 3,887,914, April 15, 1975 Ib issued by Irgensbergh, 3 887 918, April 15, 1975 Thomas A Cerbo issued, 3,907,537, on September 23, 1975 Ib Von Irgensbergh and 4,046,548, September 6, 1977 Thomas K. Wood et al. granted, discussed in detail.

The Coating of the inorganic non-metallic particles is suitably by numerous means known in the art causes. The silver coating, for example, by fluidization over dry or wet processes, electroless plating and the like applied. See, for example, U.S. Patent No. 4,777,205, La Scola issued, No. 4,822,523, Prud'Homme No. 4,836,955 issued to Ehrreich, 5,075,038 to Cole et al. and No. 5,227,093, Cole et al. issued; US Pat. No. 5 229 037, Tanaka et al. issued; and U.S. Patent No. 3,635,824, Raymond G. Brandes et al. granted.

As As noted above, any type of particulate filler will be used conductive made by applying a layer of an effective amount of conductive material is deposited on it. The conductive material is any suitable conductive Substance and may, for example, a metal, a metal alloy or another metal-containing substance. Consequently, it is the electrically conductive Material preferably a noble metal or another conductive metal, an alloy of two or more of these metals or an electric one conductive Compound, an electrically conductive Polymer or other substance containing one or more of such Contains metals. Particularly preferred are precious metals, such as. Gold, silver, platinum, Palladium, as well as other conductive Metals, such as As nickel, iron, copper, zinc, chromium, cobalt and Aluminum.

According to the preceding are the conductive ones spherical Particles preferably with conductive metal coated glass beads, in particular silver-coated glass beads containing a substantially spherical Have shape. Typically, the spherical particles have including the outer layer made of conductive Material, a size of about 10 microns to 100 microns in average diameter. Such Particles with a mean diameter of 30 microns to 70 Micrometers are particularly preferred.

The spherical Particles generally come with a conductive material in an amount from 8% to 24% by weight, preferably in one Amount of 12% by weight to 20% by weight, coated.

Likewise, the conductive metal coated elongated particles useful in the present invention are preferably conductive metal coated glass fibers. Typically, the elongated particles, including the outer layer of conductive material, have a diameter of from 1 micron to 50 microns, preferably from 10 microns to 20 microns, and most preferably 16 microns. The elongate particles have a length of 4 × 10 ^-4 m to 16 × 10 ^-4 m (1/64 inch to 1/16 inch), with 8 × 10 ^-4 m (1/32 inch) being preferred. Especially preferred elongated particles have a diameter of 16 microns and a length of 8 x 10 ^-4 m (1/32 inch). On average, the elongate particles have an aspect ratio of 40: 1 to 320: 1, with an aspect ratio greater than 80: 1 being preferred.

The elongated Particles can Coated by any known means with a conductive material or coated are, preferably metals, as described above. The amount the metal coating on the elongated Particles varies from 15% to 30% by weight, preferably from 20% to 27% by weight. In particular very preferred embodiments are the elongated ones Particles with silver coated glass fibers, wherein silver in one Amount of 15% by weight to 30% by weight and most preferably from 20% to 27% by weight.

The mentioned above Components of the particulate filler are (a) in an assembled amount and (b) in relative amounts used to each other, so that the properties discussed above ensured become. In particular, the amount of filler is such that the desired good conductivity can be realized. Typically, the conductive material is located in an amount sufficient to make the composition one resistivity of not more than 20 mOhm · cm. It is important that this is done using an electrically conductive filler most of the work is done is an inorganic material that is less expensive and which is less dense than a filler, the main one is metallic. At the same time, the relative amounts of spherical or elongated conductive Particles such that the composition containing them is adequate is flexible.

As it is impractical, a strictly numerical measure of the whole Effectiveness of the invention while maintaining flexibility in the for the electrically conductive Composition required to reach the desired level Application to work successfully, versus the flexibility of the material, if not with conductive corpuscular filler is loaded to provide. What is acceptable varies from one Application to another, etc. After this is said, it is still clear that the electrically conductive Composition have the required minimum amount of flexibility must be in order for it to be suitable in practice. The invention makes this possible Achieve this minimal amount of flexibility. Because this amount is dependent changes from the usage circumstances and can not be expressed as a general numerical parameter can, should the condition of having flexibility in at least the required minimum amount herein as "effectively flexible". A common one Professional will be able to do this (without undue experimentation or another invention), at least empirically to identify the minimum flexibility, which is required under any particular set of circumstances, and will therefore easily understand the term "effectively flexible". In particular, the Amount of corpuscular filler out to a good conductivity (as measured indirectly by the resistance), diminished however, not significantly the flexibility over that of the matrix material alone (indirectly by the durometer hardness or by other measurements physical and structural integrity measured). The conductive filler may be included in any compounded amount the for a desired one Application is suitable. Once in possession of the teachings herein, can be a common one Professional such a lot as a routine matter and without the Need for determine an innovation, invention or the like.

If a mixture of leiffähigen elongated and spherical Particles as filling material for the Compositions of the invention used became unexpected found that the conductive elongated particles and conductive spherical Particles must be present in certain amounts relative to each other, so that those with conductive Material coated particles in an electrically conductive relationship stand while still maintain the required degree of flexibility of the matrix becomes. The relationship of oblong (For example, on a fiber basis particles to spherical (for example on a bead basis) Particles are selected to trim the composition to ensure the desired flexibility. The Relationship between the conductive elongated and executable spherical Particles is called the weight ratio expressed which varies from 1: 1 to 4: 1, preferably 2: 1 to 4: 1, more preferably 3: 1.

The entire conductive Loading the compositions of the invention is also very important. Electrically conductive Compositions containing only spherical particles as filler contain a good specific electrical Resistance (low value) ready. The flexibility of the matrix, how due to high durometer hardness values however, is low and undesirable for many applications. Around a good electrical resistivity only with spherical particles as filler to reach are also pretty high overall conductive Loads required. Total conductive loads below 69 Weight percent, the only spherical Particles as conductive For example, using material does not confer adequate conductivity. Surprisingly However, it was found that when a mixture of elongated and spherical Particles in conductive Relationship is used, good specific electric values Resistance can be obtained with lower total conductive loads can, otherwise deemed necessary if only spherical Particles for a conductive one Bead filler be used. The total conductive loading for the compositions of the invention is from 40% to 70% by weight, preferably 50 percent by weight to 60 percent by weight, and more preferably 50 percent by weight up to 55% by weight. It goes without saying that the previous one for cost savings and a lower specific weight to lead can.

The The aim of the present invention is to provide compositions to provide the superior Have properties including, among others, good electrical conductivity and good flexibility. The electrical conductivity can be measured in terms of electrical resistivity be, with a low specific electrical resistance on a high electrical conductivity indicates and vice versa. The flexibility can be measured as durometer hardness with lower durometer values becoming more flexible, less rigid Compounds correspond.

electrical conductive Compositions according to the present invention Invention show an excellent initial specific electrical Resistance, typically in the range of 10 mΩ · cm to too, but not inclusive 200 mΩ · cm at a medium durometer hardness from 50 to 70 on the "D" scale. In particular good embodiments has the electrically conductive Composition a specific electrical resistance of not more than 20 mΩ · cm and a medium durometer hardness of not more than 70 on the "D" scale. Other good compositions show a similar specific electrical Resistance at an average durometer hardness that is 8% to 30% lower is considered the flexible matrix material that only spherical particles contains sufficient to provide a specific electrical resistance, which is comparable to that of the compositions of the present invention is.

One Another important advantage of the invention is that the Precursor material favorable has rheological properties. Consequently, it is sufficient flowability or other deformability to be shaped as needed In order to make the design of the electrically conductive composition to a desired To allow shape. The precursor material is typically in the form of a paste, however, it may also be a liquid in certain embodiments be.

It is not practical, a strictly numerical measure of whether a precursor material is malleable or instead, viscous, stiff or otherwise unyielding is to provide. As can be seen, that varies, which is acceptable from one application to another, etc. However, it is obvious that a common professional for any special set of conditions will know if a specific precursor material a has suitable formability or not. The practice of the invention allows the achievement of such moldability. For the purpose of simplicity In the expression, the condition is to have sufficient Moldability to allow the precursor material to be configured as desired can be, then referred to herein as "effective malleable " become. A common one Professional will be able to do this (without undue experimentation or further invention), at least empirically the minimal formability to identify under any specific set of conditions is required and will therefore easily understand the term "effectively malleable".

EXAMPLES

The The following examples serve to provide a further assessment of the Invention, but in no way their effective scope limit. The physical properties were measured at room temperature unless otherwise stated or clear from the context.

materials and procedures

Certain The examples described below demonstrate the invention and therefore involve the use of both spherical conductive particles as well as elongated ones conductive Particles. Other of the examples demonstrate control embodiments, in which either spherical or oblong conductive Particles, but not both, were used.

For all following Examples were the physical properties, such. B. initial specific electrical resistance and hardness, measured on strips, which have been cut from seals made of the electrically conductive composition of the present invention.

Several different classes of silver-covered glass beads were called spherical conductive particles in the example embodiments used. These were the class numbers S-3000-S2, S-3000-S4, S-3000-S5 and S-2530-S4, all from Potters Industries, Inc., are commercially available. The S-3000 Series particles include medium-sized glass beads Diameter of 30 μ, while the particles of the series S-2530 glass beads with a middle Diameter of 66 μ. The silver coating on the glass beads was 8, 16 and 20 percent by weight, respectively for the Classes S-3000-S2, S-3000-S4 or S-3000-S5. The silver weight percentage for S-2530-S4 was 16% by weight.

Silver coated glass fibers were used as conductive elongate particles in the example embodiments. The coated fibers used were Fibertec Particles T-3082, T-3032 and T3016, all of which are commercially available from Potters Industries Inc. The coated fibers T-3082 and T-3032 have a diameter of 16 μ and the particles T-3016 have a diameter of 10 μ. The coated fibers T-3016 having a length of 16 × 10 ^-4 m (1/16 inch) and the coated fibers T-3082 has a length of 4 x 10 ^-4 m (1/32 inch). The bulk density of T-3032 was different from that of T-3082. The fibers had an aspect ratio of about 50: 1 to about 160: 1.

The Seals tested were prepared by mixing samples of silicone rubber SE-6370 and SE-6350 as available from General Electric Co., coated with silver-coated glass fibers and / or silver-coated beads as described above. A curing organoperoxide catalyst, namely dicumyl peroxide, Dibenzoyl peroxide or MEK peroxide, was added to the reaction mixture integrated at room temperature, although the catalyst also at elevated temperature could have been admitted if desired. The amount of catalyst can be determined by one skilled in the art without exercising one invention and is typically based on the desired actual cure rate, Working life and the like. Organoperoxide catalysts which are miscible with the silicone rubber rubber, were in a Amount of about 0.5-1% on the total weight of the composition on the basis of the total amount used of silicone rubber rubber.

The mixing was performed using a Brabender ^® Plasticorder kneader and the amounts of conductive particulate filler were selected to provide target weight percent of the total conductive loading in the electroconductive composition. The manner of adding the conductive material to the silicone rubber rubber is not essential. (In the examples demonstrating the invention, silver-covered glass beads were added first, followed by the addition of silver-covered glass fibers; a reverse order of addition may also work.) The resulting curable mixture of silicone rubber rubber, conductive filler particles, and organo-rubber. Catalyst was then placed in a seal mold where it was pressed at 9070 kg (20,000 lbs.) Pressure and at 176.67 ° C (350 ° F) for about 30 minutes, then allowed to cool. A gasket was made which was 0.178m (7 inches) long, 0.178m (7 inches) wide and about ^{20x10 -4m} (0.08 inches) thick. Subsequently, the gasket was placed in an oven at about 200 ° C for a period of about 1 hour to about 4 hours for postcuring, ie, to drive off the volatiles. Four or five strips, each 0.102m (4 inches) long, 127 x 10 ^-4 m (0.5 inches) wide and about 20 x 10 ^-4 m (0.08 inches) thick, were prepared for use as specimens in measuring the physical properties, such. Of the initial resistivity and hardness, cut from each seal. In particular, the surface resistance of the strips of each seal was measured with a Walhalla Model 4100 OTC resistance meter at four or five locations on each strip, and from these values and the measured thickness, a mean initial volume resistivity was calculated for each seal. The hardness of each sample was measured using a Gardner Scientific Durometer.

EXAMPLES 1-18

seals were prepared as described above in the section titled "Materials and Methods". For each For example, the following data was recorded: the initial one Hardness of Silicone rubber, the total conductive loading of the composition, the weight percent of beads and / or fibers in the electrically conductive composition which Percent by weight of silver coating on the beads and / or fibers, the initial specific electrical resistance of the electrically conductive composition in mΩ · cm and their hardness, as measured in durometer scales A and D.

The Table 1 below summarizes the processing parameters and test results for the tested embodiments together.

Examples 5, 7, 11, 13 and 16-18 show physical properties of the electroconductive compositions of the invention wherein the conductive filler is a mixture of elongated particles and spherical particles both coated with silver as a conductive material. In these examples, the elongated conductive particles were silver-coated glass fibers 16 μ in diameter and 4 x 10 ⁴ m (1/32 inch) long as supplied by Potters Industries Inc. as Fibertec T-3082. The conductive coating on the fibers varied from about 20 weight percent to about 30 weight percent Silver. Likewise, the conductive spherical particles were silver-coated glass beads having an average diameter of 30 μ and a silver coating varying from about 8 weight percent to about 20 weight percent, with the exception of example 17, in which the silver-coated beads of the filler had a diameter of 66 μ had. Compared with the sample tested in Example 16, the initial electrical resistivity improved (decreased) when using larger diameter beads.

On the other hand, Examples 1-4, 6, 8-10, 12, 14 and 15 show the physical properties of various control embodiments performed with gaskets made using not a combination of electrically conductive elongate particles and electrically conductive spherical particles, but instead only spherical conductive particles or only elongated conductive particles were produced. Specifically, Examples 1 and 3 are directed to only electrically conductive silver-coated beads having an average diameter of 30μ (commercially available from Potters Industries, Inc.). The silver coating was 16% by weight and the matrix materials were GE Corporation's silicone rubber gum having an initial hardness of 70 and 50, respectively. The remainder of the control embodiments were gaskets containing only elongated electrically conductive particles, namely silver coated glass fibers as described by Potters Industries Inc commercially available. The fibers had a diameter of 16 μ and a length of about 4 x 10 ⁴ m (1/32 inch) with an aspect ratio of 60: 1. The silver content of the coating for these fibers varied from about 8 weight percent to about 44 weight percent.

EXAMPLES 19-26

Similar tests were conducted on control embodiments and embodiments according to the present invention wherein the conductive filler contained conductive elongated particles having a higher aspect ratio than those used as conductive filler in Examples 1-18. In particular, Examples 21-24 were for the use of conductive elongate particles, such as e.g. As Fibertec T-3016, as supplied by Potters Industries, Inc., having a diameter of 10 μ and a length of 16 × 10 ^-4 m (1/16 inch) with a coating, which formed 24 per cent by weight of the particle, directed. Table 2 below summarizes the initial resistivity and hardness values obtained for the gaskets of Examples 19-26, each of which has the aspect ratios given in the table.

Examples 19, 20, 25 and 26 are directed to the control embodiments mentioned above. In Control Examples 19 and 20, the samples consisted of gaskets made in accordance with the section entitled "Materials and Methods" above except that the conductive filler was not formed a mixture of electrically conductive elongated and spherical particles. In particular, the gaskets tested in Examples 19 and 20 were made from an electrically conductive composition containing as conductive filler only silver-coated fibers having a total conductive loading of 50% and 55%, respectively. In addition, in Control Embodiments 25 and 26, the conductive filler consisted only of elongated particles of slightly larger diameter, ie, silver coated fibers, commercially available from Potters Industries, Inc. under Fibertec T-3032. These fibers had an aspect ratio of 60: 1.

As from Table 2 above and from Table 1 is readily apparent, improved (decreased) the initial specific electrical Resistance when the ratio the elongated one Particles to the spherical ones Particles 3: 1, especially for a total conductive loading from about 55% to about 60% by weight. It was also the silicone rubber with 50 durometer also softer and therefore more flexible made. This is supported by Examples 5 and 6.

Claims (17)

Electrically conductive composition which an elastic matrix material and a corpuscular filler which is distributed in the matrix material, wherein the corpuscular filling material a variety of elongated Particles having a core or a substrate, which / s with a conductive Material is coated, and a variety of spherical particles having a core or a substrate, which / s with a conductive Material is coated, with the elongated particles and the spherical particles are essentially mutually mixed, the total amount of corpuscular filling material 40 to 70 weight percent of the composition is and that weight ratio the elongated one Particles to the spherical ones Particles in a range of 1: 1 to 4: 1, leaving the conductive particles in electrically conductive Connection to each other and so that the electrically conductive composition functionally flexible is. A composition according to claim 1, wherein the weight ratio of elongated Particles to the spherical ones Particles in a range of 2: 1 to 3: 1. Composition according to one of the preceding Claims, being the elongated one Particles with electrically conductive Material coated glass fibers have. A composition according to any one of the preceding claims, wherein the elongate particles have a length of 4 x 10 ^-4 m to 16 x 10 ^-4 m (1/64 to 1/16 inch) and a diameter of 1 to 50 microns. Composition according to one of the preceding Claims, being the elongated one Particles have an average aspect ratio of 40: 1 to 320: 1. Composition according to one of the preceding Claims, the coated spherical ones Particles with electrically conductive Material beschitete glass beads exhibit. Composition according to one of the preceding Claims, the coated spherical ones Particles have an average diameter of 10 to 100 microns. Composition according to one of the preceding Claims, being the elongated one Particles or the spherical ones Particles coated with a metal are selected from the group selected which is composed of Ag, Au, Pt, Pd and Cu. A composition according to claim 10, wherein the elongated Particles coated with silver in an amount of 15 to 30 percent by weight are or the spherical ones Particles with a conductive Metal coated in an amount of 8 to 24 percent by weight are. A composition according to claim 9, wherein the elongated Particles coated with silver in an amount of 20 to 27 percent by weight are or the spherical ones Particles coated with silver in an amount of 12 to 20 percent by weight are. Composition according to one of the preceding Claims, wherein the composition has a specific electrical resistance of not more than 20 mΩ · cm. Composition according to one of the preceding Claims, wherein the composition has an average durometer hardness of not less than 70 on the "D" scale. An article of manufacture which is a molded element comprising an electrically conductive composition according to a of the preceding claims having. Article according to claim 13, wherein the article is formed by injection molding. Article according to claim 13 or 14, which is a molded gasket. An electrically conductive paste which is one to a elastic matrix material formable precursor material and distributed in the precursor material corpuscular filling material wherein the particulate filler comprises a plurality of elongated Particles having a core or a substrate, which / s with a conductive Material is coated, and a variety of spherical particles having a core or a substrate, which / s with a conductive Material is coated, with the elongated particles and the spherical particles are essentially mutually mixed, the total amount of corpuscular filling material in the paste and the amounts of elongated particles and spherical particles relative to each other are designed so that when the precursor material is formed to the matrix, the conductive particles are in electrical conductive Connection to each other and the thus formed electrically conductive Composition functionally flexible is. Paste according to claim 16, wherein the ingredients are defined in any one of claims 1 to 10.